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Date:   Mon, 31 Dec 2018 14:48:34 -0500
From:   Theodore Ts'o <>
To:     Ext4 Developers List <>
CC:     Theodore Ts'o <>, <>
Subject: [PATCH 1/3] ext4: avoid kernel warning when writing the superblock to a dead device

The xfstests generic/475 test switches the underlying device with
dm-error while running a stress test.  This results in a large number
of file system errors, and since we can't lock the buffer head when
marking the superblock dirty in the ext4_grp_locked_error() case, it's
possible the superblock to be !buffer_uptodate() without
buffer_write_io_error() being true.

We need to set buffer_uptodate() before we call mark_buffer_dirty() or
this will trigger a WARN_ON.  It's safe to do this since the
superblock must have been properly read into memory or the mount would
have been successful.  So if buffer_uptodate() is not set, we can
safely assume that this happened due to a failed attempt to write the

Signed-off-by: Theodore Ts'o <>
 fs/ext4/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d6c142d73d99..fb12d3c17c1b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4902,7 +4902,7 @@ static int ext4_commit_super(struct super_block *sb, int sync)
 	if (sync)
-	if (buffer_write_io_error(sbh)) {
+	if (buffer_write_io_error(sbh) || !buffer_uptodate(sbh)) {
 		 * Oh, dear.  A previous attempt to write the
 		 * superblock failed.  This could happen because the

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